Protective coating material



Eatented Aug. 18, 1953 PROTECTIVE COATING MATERIAL Benson G. Brand, Columbus, Ohio, assignor, by

mesne assignments, to The Battelle Development Corporation, Columbus, Ohio, a corporation of Delaware No Drawing. Application. October 11, 1950, Serial No. 189,665

4 Claims. (Cl. 260-23) This is a continuation-in-part of application Serial No. 140,794, entitled Carbon Film Resistor, and filed January 27, 1950.

This invention relates to protective coating materials .and, more particularly, to an air-impervious protective coating material and to its method of manufacture.

Electrical components such as capacitors, transformers. coils, insulators, resistors, and others, are frequently subjected, in operational use, to the effects of injurious atmospheres, or other injurious external conditions. It has been proposed to protect such electrical elements by coating such elements with a protective coating material. The protective coating material constituting a part of the subject matter of this invention is ideally suited for such use, offering protection to such electrical components of a degree never enjoyed before.

Furthermore, this protective coating material is particularly adapted for use in the protection of film type resistors having resistive material which is subject to oxidation, such as carbon-film resistors. Such carbon-film resistors previously had been inoperable at high temperatures, such as those in the vicinity of 200 C. Carbon-film resistors which were exposed to such temperatures in an oxidizing or other injurious atmosphere very rapidly deteriorated, usually due to oxidation, and failed to serve their useful purpose. Obviously, a protective coating material applied to such a resistor, and which would be airimpervious at such high temperatures, might serve to prevent such breakdown of the carbon film. However, protective coatings of the prior art are unsatisfactory for such purposes because they either fail to protect the carbon film at such an. operating temperature, or even if they initially offerv some protection to the carbon film, after a short period of operational time, they break down, thereby exposing the carbon film to high temperature and injurious atmospheres which cause the carbon film to oxidize or otherwise deteriorate. Where it is desired to use a carbon-film resistor at a temperature of at least 200 C., for a period of time as long as 400 hrs, with a percent variation in resistance of the resistor of or less, protective coating materials of the prior art have proven unsatisfactory.

It is, therefore, one object of this invention to provide an improved protective coating for a film type resistor.

It is another object of this invention to provide a protective coating material for a carbon-film resistor which will enable such a resistor to be operated at a temperature of 200 C. for a period of 400 hrs., without having the resistance of such a resistor vary more than 10% in value.

It is still another object of this invention to provide a protective coating material which may be used to protect any electrical component from injurious, external action.

It is a further object of this invention to provide an improved method of making such a protective coating material.

Various additional objects and advantages of this invention will become apparent from the'following description.

There has been discovered that a protective coating material prepared from a cyclic, hydrocarbon resin is extremely satisfactory for coating carbon-film resistors, or other readily oxidizable film resistors, where such resistors are to be used in injurious or oxidizing atmospheres and at high temperatures.

By cyclic, hydrocarbon resins is meant the following representative compounds:

Polystyrene H H ..C O

1'5 Polyterpene 1 H C. Q

Coumarone indene Such cyclic, hydrocarbon resins may be used in conjunction with a drying oil to provide a varnish which is useful as a protective coating material, or which after admixture with certain ingredients may be made into a protective coating material which can be used to coat an oxidizable film resistor.

The degree of polymerization of the various cyclic, hydrocarbon resins constitutes a limit on the scope of this invention only when the resins are not soluble in a drying oil. Moreover, all known grades of the above-mentioned resins, that are soluble in a drying oil, may be used. Furthermore, any quantity of resin may be combined with any quantity of drying oil to provide a varnish, as long as all of the resin can be dissolved in the drying oil. However, because of the difficulty encountered in forming a varnish when extremes of the two ingredients are used, it is preferred to use from 35 to 60% of the resin on a weight basis, and the balance drying oil, in the preparation of the varnish. While these percentages of resin will produce a superior varnish, the ideal quantity is approximately 51% resin, by weight, the balance a drying oil.

The varnish is formed by heatingv the. dryingoil and the resin at a temperature between an:

proximately 225 C. and 250 C. until a varnish is obtained. The standard pill test is used to determine when the varnish has been obtained. This test is performed by placing a drop of the varnish on a sheet of clean cold glass to form a pill and then forming a string from that pill. When a three-foot string can be formed, the varnish is considered completed.

The varnish thus formed then has added thereto a quantity of thinner sufficient to make the varnish workable. The quantity added will depend upon the particular varnish. It is preferred to combine approximately equal weights of thinner and varnish non-volatile. The thinner should be volatile and its primary function is well known in the art, namely, to reduce the viscosity of the previous mixture to a workable state. Thinner which may be used include xylene, toluene, and benzene. Petroleum products such as aliphatic napthas may also be used. The preferred thinner is xylene.

The protective coating material thus formed may then be applied to an electrical component. If desired, it may first be further thinned.

While such a thinned varnish is a good protective coating material, it is. preferred to add to the thinned varnish a quantity of mica, preferably leafing-type mica. The particle size of this material i not critical and does not materially affect the quality of the resultant product. Based on the non-volatile weight, i. e., the weight prior to the addition of a thiriner, sufiicient mica may be added to the varnish to create a protective coating material containing approximately 50% mica. The preferred composition, however, comprises 72% varnish andthebalance mica, on a non-volatile basis. The resultant protective coating material, which may befurther thinned if necessary, and which is one embodiment of the protective coating material, may be applied to an electrical component by brushing, spraying, dipping, or other. satisfactory method.

In addition to leaiing-type mica, such materials as titanium dioxide and ground barytes are also useful additives. Here again the particle size of these materialsis not critical. A preferred protective coating material comprises, based on the non-volatile weight, from approximately 35% to 85% by weight of varnish, the balancebeing from to 90% by weight ofinica, andfrom 80% to 10% by. weight oftitanium dioxide. A preferredexact compositioncomprises 65% varnish, 10%. titanium dioxide, and mica on a non-volatile basis. Such protective coatingmaterial may be applied by brushing, spraying; dipping, etc. v Q

It is to be understoodthatthis protective coating material may. beiurther modified by the-addition of ground barytes. It is preferred not to add in excess of approximately 25% barytes, and a preferred composition of a protective coating material containing barytes would comprise 65% varnish, 12 mica, 12 /2% barytes, and 10% titanium dioxide, on a non-volatile basis.

To illustrate the method of making such a protective coating material and to enable one skilled in the art to perform this invention, the following examples, are given. It is to be understood that these examples are merely illustrative and should in no. way be construed as limitations on the scopeof the disclosure herein.

Example I 1,7; gallons of; China-wood oil and pounds of polyterpene resin were heated at a temperature of approximately 235 C. until a satisfactory varnish was obtained by means of the pill test. This varnish then had added thereto 225 pounds ofxylene. The thinned varnish then had leasingtype mica and titanium. dioxide dispersed therein, in the following proportions, based on the non-volatile Weight:

Percent Varnish 65 Titanium dioxide l0 Mica 25 This mixture was further thinned by theadd tion of 50 pounds of xylene.

The particular polyterpene resin used had. a ball and ring melting pointof 100 C,, acid number and saponification number less, than. 4, and was, composed essentially of polyme s, of; pinenes.

The u ta pr t ve coating. material was placed on a carbon-film resistor by dipping the carbonefilmresistor in the protective coatingmaterial, and then baking the coated resistor in air at 350 F. for 30,. minutes. Thisdipping and bak Was epeated w e. to, make three, successive, dips, with baking periods following each dip. A resistor so protected.withstood' morethan 400 hrs. of operation, in air,a t 200 C. under a one-watt load without changing more than-10,%. inresistance.

Examp 15 gallons-of tung oil and 1.00poundsof: coumae rone-indene: resin: were heated: at; atemperatur'e of: 242? C; until. a varnish was. obtained: by; the standard pill .test. This varnishhadadded there, to. 220 poundsof Xylene. The thinnedzvarnish then had. added. thereto leafing-type. mica ti: tanium dioxide, and-.groundzbarytes, in thatch lowing proportions, based: onthenon-volatile weight: 7

Percent Varnish 65 Mica 12 /2 Barytes 12 /2 Titanium dioxide.- 10

at least 100 hours of operation in air at 200 C. under a one-watt load without changing more than in resistance.

It should be apparent from the above description that there has been devised a novel, air impervious, protective coating material, and a novel method of manufacturing such a material. Such a protective coating material, when used to coat a carbon-film resistor, or any other easily-oxidizable resistor, materially increases the useful life of such a resistor at high-operating, temperatures in oxidizing or other injurious atmospheres. Such a protective coating material may also be effectively used to protect and prolong the life of other electrical components.

In its commercial form the finished material may include small quantities of driers, such as cobalt napthenate, manganese napthenate and lead napthenate, either singly or in combination, as would be well known to those skilled in the art.

While this invention has been described in its preferred embodiment it is to be understood that the words used are words of description rather than words of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention.

What is claimed is:

1. The method of making a protective coating material which comprises heating from 65% to 40% of a China-wood oil and from 35% to 60% of polyterpene resin to a temperature between 230 C. and 245 C. to form a varnish; thinning said varnish with a suitable solvent; and thereafter mixing from 35% to 85% of said thinned varnish, based on the non-volatile weight, with a material comprising from 20% to 90% mica and the balance titanium dioxide.

2. The method of making a protective coating material which comprises heating from 65% to 40% of a China-wood oil and from 35% to 60% of polyterpene resin to a temperature between 230 C. and 245 C. to form a varnish; adding sufiicient xylene to said varnish to make said 6 varnish workable; and mixing said thinned varnish with leafing-type mica and titanium dioxide in the following proportions, based on the non-volatile weight:

Percent Varnish Mica 25 Titanium dioxide 10 Percent Varnish 65 Mica 25 Titanium dioxide 10 4. A protective coating material for an electrical component, said coating material having been made by heating from 65% to 40% of a China-wood oil and from 35% to 60% of polyterpene resin until a varnish was formed; thinning said varnish with a suitable thinner; and mixing from 35% to of said thinned varnish, based on the nonvolatile weight, with a material comprising from 20% to leafing-type mica and the balance'titanium dioxide.

BENSON G. BRAND.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,019,666 Lender et a1 Mar. 5, 1912 1,492,155 Brown Apr. 29, 1924 1,587,333 King June 1, 1926 2,380,456 Maier et a1 July 31, 1945 2,482,086 Foster Sept. 20, 1949 

1. THE METHOD OF MAKING A PROTECTIVE COATING MATERIAL WHICH COMPRISES HEATING FROM 65% TO 40% OF A CHINA-WOOD OIL AND FROM 35% TO 60% OF POLYTERPENE RESIN TO A TEMPERATURE BETWEEN 230* C. AND 245* C. TO FORM A VARNISH; THINNING SAID VARNISH WITH A SUITABLE SOLVENT; AND THEREAFTER MIXING FROM 35% TO 85% OF SAID THINNED VARNISH, BASED ON THE NON-VOLATILE WEIGHT, WITH A MATERIAL COMPRISING FROM 20% TO 90% MICA AND THE BALANCE TITANIUM DIOXIDE. 